There has long been an interest in equipping computers with wireless communications capability, but only recently has such capability been viewed as a necessity. The proliferation of powerful, portable electronic devices has created a commensurate need for facilitating communication between these devices. Existing interface cables have proven to be cumbersome and limiting. Accordingly, system designers now provide a wireless communications capability for most modern portable electronic devices.
Five major types of (portable) wireless communications capability exist today: infrared ports, wireless personal area networks (WPANs), wireless local area networks (WLANs), cellular or wireless wide area networks (WWANs), and satellite. Devices equipped with infrared ports communicate through the use of infrared signals, while devices using the other four major types of wireless communications communicate through the use of radio frequency (RF) signals. Infrared signals are easily blocked, and the typical communications range is very limited (e.g., about 5 meters). WPANs generally use very low power RF signals, which typically limits the communications range to approximately 10 meters or so. (Their target application is cable replacement.) WLANs are wireless alternatives to wire-based local area networks (LANs), and their range is approximately 100 meters. The communications range of cellular devices is substantially greater (about 20 kilometers), and they rely on a network of cellular base stations to communicate anywhere the telecommunications network will reach. Similarly, satellite phones can access a base station several thousand kilometers away via a network of earth-orbiting satellites, and communicate anywhere the telecommunications network will reach.
In wireless communications, the energy transmitted to a receiving device falls off rapidly as the distance from the transmitting device increases. The environment around the transmitting and receiving devices comprises various objects that cause reflection and attenuation. One proven method for addressing such problems is antenna diversity. When a receiving device is provided with an array of antennas, the receiving device can combine signals from the various antennas in such a manner as to “focus” the array on the transmitting device in some cases, or in other cases, to simply enhance sensitivity in certain directions while suppressing sensitivity in other directions. The directional characteristics of antenna arrays allow for improved signal reception and more reliable wireless communications.
Unfortunately, several obstacles exist to incorporating antenna diversity techniques in portable devices. Such devices may be usable in a variety of orientations, causing the antenna array's orientation to be altered undesirably. The relative position of the device's user may change, thereby affecting the reception of one or more antennas in the array. The portable device's physical size is typically minimized, limiting the antenna spacing. Finally, the portable device may have limited resources, limiting processing power and speed for adapting the antenna array's configuration.